The present invention relates to a novel photoresist composition containing a photoextinction agent suitable for fine processing of semiconductor devices or, in particular, to a photoresist composition capable of maintaining its high performance even by the prebaking carried out at an elevated temperature.
Various kinds of electronic devices such as transistors, ICs, LSIs and the like are manufactured by fine processing on the surface of substrates such as high-purity silicon semiconductors utilizing the techniques of photoetching. The procedure for the preparation of electronic devices by the photoetching techniques is carried out by first providing a layer of a photoresist on the surface of a wafer of silicon semiconductor, overlaying the photoresist layer with a mask or a transparency bearing desired image-wise patterns, exposing the photoresist layer through the mask or transparency to give image-wise exposure, developing the thus exposed photoresist layer to leave the pattern-wise layer of the photoresist followed by etching and selective diffusion on the etched areas to impart desired characteristics. It is usual that the above described processes are repeated several times each with a selective diffusion followed by providing electrodes and wiring connection with aluminum deposited on suitable portions of the surface giving a final electronic device.
One of the difficult problems in the above procedures utilizing a photoresist composition is as follows. When the step of the selective diffusion is repeated several times on a wafer surface, there can often be produced a step-like difference in the surface level of 1 .mu.m or larger and this step-like height difference on the surface is further increased by the subsequent passivation treatment. It is rather a difficult problem to obtain a fine wiring of aluminum of a few .mu.m or finer with high fidelity on such a rugged surface by the techniques of deposition of aluminum and photoetching as described above, especially, when the photoresist composition is a negative type one due to the strong halation in the photoresist layer by the irregular reflection of the incident light projected perpendicularly to the wafer surface at the sloped portions around the steps on the rugged surface with high reflectivity of the aluminum.
Various attempts have been undertaken to reduce the halation in the photoresist layer in order to reproduce very fine patterns of the photoresist with high fidelity, among which addition of a photoextinction agent is the most promising way (see, for example, Japanese Patent Publication No. 51-37562).
With a solution type photoresist composition formulated, for example, with a cyclized rubber and a bisazide compound as a crosslinking agent, however, there is a limitation in the use of a hitherto known photoextinction agent added to the composition due to the sublimation or dissipation of the photoextinction agent in the course of prebaking carried out at an elevated temperature. Namely, a treatment of prebaking of a substrate coated with a solution type photoresist composition is indispensable in order to completely remove any trace amount of the residual solvent from the photoresist layer to enhance the adhesion of the photoresist layer to the substrate surface while the conventional photoextinction agent such as Oil Yellow which is an organic dyestuff is readily dissipated at the prebaking temperature of 80.degree. to 100.degree. C. so that the halation preventing effect is greatly reduced or, if not reduced so far, subject to variation according to the uncontrollable conditions in the prebaking treatment. Lower temperatures of prebaking treatment are usually unsatisfactory because, although the loss of the photoextinction agent by decomposition or dissipation can be avoided, the remaining solvent left in the photoresist layer may result in decreased adhesion of the photoresist layer to the substrate surface as well as in the appearance of ripples in the photoresist layer after development.
Several kinds of bisazo compounds have been proposed as expressed by the following structural formulas as the photoextinction agents to be formulated in a photoresist composition with a cyclized rubber as the base component. ##STR1##
These compounds have good compatibility with cyclized rubbers and do not sublimate so that they are excellent as a photoextinction agent for preventing halation in the photoresist layer. They are, however, disadvantageous from the practical standpoint because they are too expensive by the difficulties in the synthetic preparation owing to their very complicated chemical structures.